Communication methods and systems for nonlinear multi-user environments

ABSTRACT

An electronic receiver comprises a nonlinear distortion modeling circuit and a nonlinear distortion compensation circuit. The nonlinear distortion modeling circuit is operable to determine a plurality of sets of nonlinear distortion model parameter values, where each of the sets of nonlinear distortion model parameter values representing nonlinear distortion experienced by signals received by the electronic receiver from a respective one a plurality of communication partners. The nonlinear distortion compensation circuit is operable to use the sets of nonlinear distortion model parameter values for processing of signals from the plurality of communication partners. Each of the sets of nonlinear distortion model parameter values may comprises a plurality of values corresponding to a plurality of signal powers. The sets of nonlinear distortion model parameters may be stored in a lookup table indexed by a signal strength parameter.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.14/847,841 titled “Communication Methods and Systems for NonlinearMulti-user Environments”, which is a continuation of U.S. patentapplication Ser. No. 14/600,310 titled “Communication Methods andSystems for Nonlinear Multi-user Environments” filed on Jan. 15, 2015(U.S. Pat. No. 9,130,637), which claims priority to U.S. provisionalpatent application 61/929,679 titled “Communication Methods and Systemsfor Nonlinear Multi-user Environments” filed on Jan. 21, 2014, nowexpired. Each of the above referenced documents is hereby incorporatedherein by reference in its entirety.

INCORPORATION BY REFERENCE

The entirety of each of the following applications is herebyincorporated herein by reference:

U.S. patent application Ser. No. 14/481,108 titled “Adaptive NonlinearModel Learning” filed on Sep. 9, 2014.

BACKGROUND

Conventional communication methods and systems suffer severe performancedegradation in the presence of nonlinear distortion. Further limitationsand disadvantages of conventional and traditional approaches will becomeapparent to one of skill in the art, through comparison of such systemswith some aspects of the present invention as set forth in the remainderof the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

Systems and methods are provided for communications in nonlinearmulti-user environments, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A and 1B depict two example configurations of a cabletelevision/DOCSIS network in which adaptive nonlinear distortion modelsare used for improving communication performance.

FIGS. 2A and 2B depict a direct broadcast satellite (DBS) network inwhich adaptive nonlinear distortion models are used for improvingcommunication performance.

FIG. 3A depicts components of an example receiver for single-carriercommunications in which adaptive nonlinear distortion models are usedfor improving communication performance.

FIG. 3B depicts components of an example receiver for orthogonalfrequency division multiplexed (OFDM) communications in which adaptivenonlinear distortion models are used for improving communicationperformance.

FIG. 4 depicts components of an example receiver operable to performmutual sequence estimation of multiple concurrent streams using anadaptive nonlinear distortion model.

FIG. 5 is a flowchart illustrating an example process for determiningnonlinear distortion model parameter values for a plurality of signalsources.

FIG. 6 is a flowchart illustrating an example process for handlingnonlinear distortion in a multiuser environment.

FIG. 7 depicts look-up tables of nonlinear distortion model parametervalues.

FIG. 8 depicts a look-up table of nonlinear distortion model parametervalues.

DETAILED DESCRIPTION OF THE INVENTION

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. In other words, “xand/or y” means “one or both of x and y”. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means“one or more of x, y and z”. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, circuitry is “operable” to perform a function wheneverthe circuitry comprises the necessary hardware and code (if any isnecessary) to perform the function, regardless of whether performance ofthe function is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, etc.).

FIGS. 1A and 1B depict two example configurations of a cabletelevision/DOCSIS network in which adaptive nonlinear distortion modelsare used for improving communication performance. In each of FIGS. 1Aand 1B there is shown a headend with cable modem termination system(CMTS) 100 comprising a transmitter 102 and a receiver 103; a hybridfiber-coaxial (HFC) network comprising a fiber optical cable 115, afiber node 106, coaxial cable 107, a repeater 108, a coaxial cable 109,a splitter 110, and coaxial cables 111A and 111B; a cable modem 112Acomprising a receiver 114A and a transmitter 116A; and a cable modem112B comprising a transmitter 116B and a receiver 114B.

Nonlinear distortion introduced by the transmitter 102 is expressed asNL1, nonlinear distortion introduced by receiver 103 is expressed asNL2, nonlinear distortion introduced by the fiber node 106 is expressedas NL3 (for simplicity of illustration the nonlinear distortionintroduced by fiber node '06 is assumed to be symmetric, but suchsymmetry need not be the case), nonlinear distortion introduced by therepeater 108 is expressed as NL4 (for simplicity of illustration thenonlinear distortion introduced by repeater 108 is assumed to besymmetric, but such symmetry need not be the case), nonlinear distortionintroduced by the splitter 110 is expressed as NL5 (for simplicity ofillustration the nonlinear distortion introduced by splitter 110 isassumed to be symmetric, but such symmetry need not be the case),nonlinear distortion introduced by the receiver 114A is expressed asNL6, nonlinear distortion introduced by the transmitter 116A isexpressed as NL7, nonlinear distortion introduced by the transmitter116B is expressed as NL8, and nonlinear distortion introduced by thereceiver 114B is expressed as NL9. For simplicity of illustration, thecables 115, 107, 109, 111A, and 111B are assumed to exhibit linearperformance, but such need not be the case.

Each of the receivers 103, 114A, and 114B comprises a nonlineardistortion compensation circuit 104 and an adaptive nonlinear distortionmodeling circuit 105. Each of the modeling circuits 105 uses one or morenonlinear distortion models to estimate/reproduce the nonlineardistortion experienced by the traffic received via its respectivereceiver. A nonlinear distortion model used by circuit 105 may have oneor more parameters associated with it which may be used for adapting thenonlinear distortion model to the particular circumstances. For example,a nonlinear distortion model may have a parameter ρ representing theAM/AM distortion and a parameter φ representing the AM/PM distortion.The values of these parameters to be used for any particular sample of areceived signal may depend on the power of the particular sample. Whichvalue of these parameters should be used for any particular power levelmay adapt over time based on error between the actual nonlineardistortion experienced by samples of the received signal and theestimated/reproduced nonlinear distortion. Accordingly, the parametersvalues may, for example, be stored in a lookup table indexed bytransmit-device identifier (e.g., MAC addresses).

In an example implementation, each of the circuits 105 may be operableto use a plurality of nonlinear distortion models at any given time. Insuch an implementation, the nonlinear distortion modeling circuit 105may, for example, be operable to select from among the plurality ofdistortion models based on which model works best (results in leasterror between actual and estimated nonlinear distortion) for any givensignal at any given time. Which model works best for a given receivedsignal may, for example, depend on the device from which the signal wasreceived. Accordingly, nonlinear distortion model parameter values may,for example, be stored in a lookup table indexed by transmit-deviceidentifier (e.g., MAC addresses of transmitters 116A and 116B).

For example, referring to FIG. 7, where both amplitude and phasedistortion depend on instantaneous signal power, a combined AM/AM andAM/PM type distortion model may be used. Such a distortion model may becharacterized by a signal power parameter, one or more AM/AM distortionparameters, and one or more AM/PM distortion parameters. Such adistortion model may be realized by, for example, two look-up tables(LUTs) 702 and 712 were the first LUT 702 maps a value of the signalpower parameter to corresponding value(s) of the one or more AM/AMdistortion parameter(s), and the second LUT 712 maps a value of thesignal power parameter to corresponding value(s) of the one or moreAM/PM distortion parameters. The lookup tables 702 and 712 thus hold aset of nonlinear distortion parameter values for a particular signalsource (e.g., the tables 702 and 712 may reside in CMTS 100 and storeparameter values for cable modem 112A). Although an exampleimplementation using two separate LUTs is described here, the combinedAM/AM and AM/PM may be realized using a single LUT that maps a signalpower parameter to a complex valued representing both the AM/AMdistortion parameter and the AM/PM distortion parameter.

Using the polar representation of a complex variable x:

x=|x|·

,  (1)

where |x| stands for the absolute value (magnitude) of x and

(x) denotes the angle of x. The received distorted signal, y, resultingfrom transmitted signal x can be represented as (omitting timedependence for simplicity of notation (i.e., x=x(t), y=y(t))):

y={circumflex over (ρ)}(|{circumflex over (x)}| ²)·|x|·

where ρ(|x|²) and φ(|x|²) represent the AM/AM and AM/PM distortionfunctions, respectively. In case that the nonlinear distortion is verysmall, y≅x and consequently ρ(|x|²)≈1, φ(|x|²)≈0 for any x.

A reproduction or estimate of a received distorted signal (denoted ŷ)resulting from a transmitted signal x can be represented as:

{circumflex over (y)}={circumflex over (ρ)}(|{circumflex over (x)}|²)·|{circumflex over (x)}|·

where z denotes an estimate of the transmitted signal prior to applyingthe nonlinear distortion model, {circumflex over (ρ)}(|{circumflex over(x)}|²) and {circumflex over (φ)}(|{circumflex over (x)}|²) representthe estimations of ρ(|x|²) and φ(|x|²) generated by the nonlineardistortion modeling circuit 105. The combined AM/AM and AM/PM typedistortion model may thus be characterized by the signal power parameter|{circumflex over (x)}|², the AM/AM parameter {circumflex over(ρ)}(|{circumflex over (x)}|²), and the AM/PM parameter {circumflex over(φ)}(|{circumflex over (x)}|²). Referring to FIG. 7, each entry k (for0≦k≦K) of the first LUT 702 holds: (1) a specific signal power 704 _(k),and (2) the value of {circumflex over (ρ)}(|{circumflex over (x)}|²)(called out as 706 _(k)) that corresponds to the specific signal power704 _(k). Similarly, each entry k of the second LUT 712 holds: (1) thespecific signal power 704 _(k), and (2) the value of {circumflex over(φ)}(|{circumflex over (x)}|²) (called out as 716 _(k)) corresponding tothe specific signal power 704 _(k). For example, denoting the specificsignal power for entry k=0 as |{circumflex over (x)}₀|², entry 0 of thefirst LUT may store |

|² and {circumflex over (ρ)}(|{circumflex over (x)}₀|²) and the secondLUT may store |{circumflex over (x)}₀|² and {circumflex over(φ)}(|{circumflex over (x)}₀|²). In another example implementation, asignal power parameter other than |{circumflex over (x)}|² may be usedand values thereof stored in fields 704 ₀ . . . 704 _(K) of LUT 702 andfields 704 ₀ . . . 704 _(K) of LUT 712. Such alternative signal powerparameter may be, for example, a function of the signal level and/orphase such as delayed signal power level (such as delayed AM/PM), afunction of signal power at other time instances (to support a nonlineardistortion model with memory), or a filtered (convolution) of signalinstantaneous power samples.

Although FIG. 7 shows indexing parameter (the power parameter in theexamples) as being stored in the lookup table, in another exampleimplementation, the indexing parameter may not actually be stored butmay simply be calculated and then mathematically and/or logically (e.g.,through a hashing function) mapped to the memory address that holds thecorresponding distortion parameter. An example of this is shown in FIG.8 in which address generator maps values pf |{circumflex over (x)}|² tothe address in which the corresponding distortion parameter is stored.

In another example implementation, a single distortion parameteraccounting for both AM/AM and AM/PM may be stored in the lookup table.In this regard, representing the reproduction or estimate of thereceived distorted signal as

ŷ={circumflex over (x)}·{circumflex over (ρ)}(|{circumflex over (x)}|²)·e ^(j{circumflex over (φ)}(|{circumflex over (x)}|) ² ⁾,  (4)

then {circumflex over (ρ)}(|{circumflex over(x)}|²)·e^(j{circumflex over (φ)}(|{circumflex over (x)}|) ² ⁾ can bestored as a single distortion parameter, as is shown in FIG. 8.

Returning to FIGS. 1A and 1B, modeling circuit 105 in receiver 114Aattempts to estimate/reproduce the composite nonlinear distortionresulting from NL1, NL3, NL4, NL5, and NL6 that is seen bycommunications from the headend 100 to the receiver 114A.

In FIGS. 1A and 1B, modeling circuit 105 in receiver 114B attempts toestimate/reproduce the composite nonlinear distortion resulting fromNL1, NL3, NL4, NL5, and NL9 that is seen by communications from theheadend 100 to the receiver 114B.

In FIG. 1A, modeling circuit 105 in receiver 103 attempts toestimate/reproduce the composite nonlinear distortion resulting fromNL2, NL3, NL4, and NL5—the nonlinearities which are common to trafficfrom the transmitter 116A and the transmitter 116B. In thisconfiguration, although communications from TX 116A also experience NL7,and communications from TX 116B also experience NL8, NL7 and NL8 areignored for purposes of simplifying nonlinear distortion estimation andcompensation in the receiver 103.

In another example implementation, NL7 and NL8 may be very similar. Thismay be the case, for example, where cable modems 112A and 112B are thesame make and model using the same power amplifier. In such animplementation, the nonlinearities may be expressed as NL7≅NL8≅NL7′, andthe adaptive nonlinear distortion modeling circuit 105 of receiver 104may attempt to estimate/reproduce the composite nonlinear distortionresulting from NL1, N12, NL3, NL4, NL5, and NL7′. In another example,NL7′ may be an average of NL7 and NL8 or may be the common terms (e.g.,higher order terms) of NL7 and NL8, when NL7 and NL8 are expressed aspolynomials.

In another example implementation, shown in FIG. 1B, the receiver 103comprises multiple instances of circuit 105, with each instance ofcircuit 105 using a different sets of parameter values such that NL2,NL3, NL4, NL5, and NL7 are accounted for when receiving from TX 116A andNL2, NL3, NL4, NL5, and NL8 are accounted for when receiving from TX116B. (It is noted that, although multiple instances of circuit 105 areshown for clarity of illustration, in practice it may be that a singleinstance of circuit 105 is operable to maintain multiple sets ofparameter values.) As a non-limiting example: each of two instances ofcircuit 105 in receiver 103 use a nonlinear distortion model havingparameter ρ, but the first instance of circuit 105 uses a first set ofvalues for ρ, and the second instance of circuit 105 uses a second setof values for ρ. As another non-limiting example: there are twoinstances of circuit 105 and the first instance of circuit 105 uses anonlinear distortion model having parameters ρ and φ, and the secondinstance of circuit 105 uses a nonlinear distortion model havingparameters C1, C2, and C3. Thus, the first instance maintains a set ofvalues for ρ and φ while the second instance of circuit 105 maintains aset of values of C1, C2, and C3. In this example implementation, thenonlinear distortion modeling circuit 105 of receiver 103 may beoperable to select between the two sets of parameter values to choosethe set of values that best estimates/reproduces the actual nonlineardistortion at any given time and for any given received signal.

In a network in which bandwidth is allocated by a central controller(e.g., by the CMTS in the DOCSIS network of FIGS. 1A and 1B or, asanother example, by the network controller of a multimedia over coaxialalliance (MoCA) network), this switching may be enabled by the fact thatthe controller manages allocation of upstream bandwidth and thus knowswhich end systems are going to be transmitting at which times, and canload the appropriate set of parameter values accordingly.

In a network in which bandwidth is not managed by a central controllerand, thus the source of a transmission is not known ahead of time,switching between sets of nonlinear distortion model parameter valuesmay be done based on inspection of received transmissions. For example,each of the end-systems may send a unique identifier as part of apreamble. The identifier may be modulated and/or coded such that it canbe reliably demodulated/decoded without aid of the NL compensationcircuit 104 in the receiver 103. Upon identifying the source, thecorresponding set of parameter values (which was previously determined)may be selected and NL compensation circuit 104 may use the selectedparameter values for receiving the remainder of the transmission. Theset of parameter values of the identified source may have beendetermined, for example, when the device was admitted to the networkand/or during a training/update interval (e.g., triggered upon a changeto the device or the network). For example, upon a device being admittedto the network probe/training signals may be used to estimate the set ofnonlinearity model parameter values for that particular device.

In another example implementation, the nonlinearity for any particulardevice may not be stored but may be estimated anew each time a burst isreceived from the particular device. For example, each burst may carry apreamble whose signal characteristics are well suited for estimating thenonlinearity of the particular device.

For an OFDM system (e.g., DOCSIS 3.1) different subcarriers of anyparticular OFDM symbol may comprise transmissions from different endsystems. Accordingly, selection of nonlinear distortion parameter values(i.e. selection between different nonlinear distortion models and/orselection between parameter values for a particular nonlinear distortionmodel) may be performed on a per-subcarrier (orper-group-of-subcarriers) basis and per-OFDM-symbol basis. In an exampleimplementation, the parameters values used for any particular end systemmay be updated only on OFDM symbols carrying transmissions for thatparticular end system.

In an example implementation, each device in a network may, duringinitial connection setup as part of a handshaking routine to admit thatdevice to the network (e.g., ranging, auto-negotiation, and/or thelike), transmit a characterization of the nonlinear distortionintroduced by its transmitter (e.g., a previously generated set ofnonlinear model parameter values). For example, in FIGS. 1A and 1B, eachof transmitter 102, fiber node 106, repeater 108, splitter 110,transmitter 116 a, and transmitter 114 b may transmit characterizationsof the nonlinear distortion they introduce during connection setup.

In an example implementation, during a handshaking routine between afirst device previously admitted to a network and a second devicecurrently being admitted to the network (e.g., ranging,auto-negotiation, and/or the like), the first device may transmittraining/probe signals which the second device can use to generate a setof nonlinear model parameter values to use for signals from the firstdevice, and the second device may transmit training/probe signals whichthe first device can use to generate a set of nonlinear model parametervalues to use for signals from the second device

In another example implementation, a database of the devices of the HFCnetwork, along with characterizations of the nonlinear distortion theyintroduce, may be maintained and accessible by devices connected to theHFC network. For example, upon installation, the cable modems 112A mayquery such a database to learn that it will be communicating with CMTS100 via splitter 110, repeater 108, and fiber node 106. It may thenretrieve NL1, NL3, NL4, and NL5 from the database.

FIGS. 2A and 2B depict a direct broadcast satellite (DBS) network inwhich adaptive nonlinear distortion models are used for improvingcommunication performance. Shown are satellite 202, two outdoor units(ODUs) 208A and 208B and their corresponding indoor units (IDUs) 214Aand 214B. The ODU 208A comprises receiver 204A and transmitter 206A. TheIDU 214A comprises receiver 210A. The ODU 208B comprises receiver 204Band transmitter 206B. The IDU 214B comprises receiver 210B.

Nonlinear distortion introduced by the satellite 202 is expressed asNL10. Nonlinear distortion introduced by receiver 204A is expressed asNL11. Nonlinear distortion introduced by transmitter 206A is expressedas NL12. Nonlinear distortion introduced by receiver 210A is expressedas NL13. Nonlinear distortion introduced by receiver 204B is expressedas NL14. Nonlinear distortion introduced by transmitter 206B isexpressed as NL15. Nonlinear distortion introduced by receiver 210B isexpressed as NL16.

In FIGS. 2A and 2B, each of the receivers 204A and 204B comprises anonlinear distortion compensation circuit 104 and an adaptive nonlineardistortion modeling circuit 105. Each of the nonlinear distortionmodeling circuits 105 attempts to estimate/reproduce at least some ofthe nonlinear distortion experienced by the signals received by itsrespective receiver.

In FIG. 2A, the outdoor units 208A and 208B demodulate and decode thesignals from the satellite 202 and then retransmit the demodulated anddecoded data to receivers 210A and 210B. In FIG. 2B, the outdoor units208A and 208B simply downconvert the signals from the satellite 202 andthen relay the signals to the respective receivers 210A and 210B.

In FIG. 2A, nonlinear distortion modeling circuit 105 in receiver 204Aattempts estimate/reproduce the composite nonlinear distortion resultingfrom NL10 and NL11 that is seen by communications from the satellite 202to the receiver 204A.

In FIG. 2A, nonlinear distortion modeling circuit 105 in receiver 210Aattempts to estimate/reproduce the composite nonlinear distortionresulting from NL12 and NL13 that is seen by communications from the ODU208A to the receiver 210A.

In FIG. 2A, nonlinear distortion modeling circuit 105 in receiver 204Battempts to estimate/reproduce the composite nonlinear distortionresulting from NL10 and NL14 that is seen by communications from thesatellite 202 to the receiver 204B.

In FIG. 2A, nonlinear distortion modeling circuit 105 in receiver 210Battempts to estimate/reproduce the composite nonlinear distortionresulting from NL15 and NL16 that is seen by communications from the ODU208B to the receiver 210B.

In FIG. 2B, nonlinear distortion modeling circuit 105 in receiver 210Aattempts to estimate/reproduce the composite nonlinear distortionresulting from NL10, NL11, NL12, and NL13 that is seen by communicationsfrom the satellite 202 to the receiver 210A.

In FIG. 2B, nonlinear distortion modeling circuit 105 in receiver 210Battempts to estimate/reproduce the composite nonlinear distortionresulting from NL10, NL14, NL15, and NL16 that is seen by communicationsfrom the satellite 202 to the receiver 210B.

In instances that the satellite 202 relays signals from a hub 250, thenonlinear distortion (represented as NL17) may also be accounted for inthe nonlinear distortion modeling circuits 105 of the ODUs (FIG. 2A) orthe IDUs (FIG. 2B).

FIG. 3A depicts components of an example receiver for single-carriercommunications in which adaptive nonlinear distortion models are usedfor improving communication performance. Shown in FIG. 3A are ananalog/RF front-end 302, a equalization/filtering circuit 304, asequence estimation circuit 306, a decoding circuit 308 (e.g., FECdecoder), an adaptive nonlinear distortion modeling circuit 105, and adigital baseband processing circuit 322. The sequence estimation circuit306 may perform functions of the nonlinear distortion compensationcircuit 104

A signal strength indicator (SSI) circuit 310 may be implemented in thecircuit 302, in the circuit 304, and/or in the circuit 306 and mayoutput a signal 311 that is used to generate an indication 311 of thestrength at which the received signal 301 was transmitted. In an exampleimplementation, during the sequence estimation process performed bysequence estimation block 306, the SSI 310 may determine instantaneoustransmit power for each sequence that is a candidate for being thetransmitted symbol sequence that resulted in the received signal. Thatis, each candidate sequence is a known sequence from a knownconstellation and thus the instantaneous transmit power of the candidateat each symbol time is known. The instantaneous transmit power for aparticular one or more candidates may be output as indication 311. Then,the instantaneous power for each particular candidate may be used forapplying the nonlinear model to that particular candidate.

In an example implementation, the indication 311 may be used by theadaptive nonlinear distortion modeling circuit 105 to select whichnonlinear distortion model parameter values to use for a particularcandidate sequence. This may include, for example, selecting from amonga plurality of sets of nonlinear distortion model parameter valuesmaintained by the nonlinear distortion modeling circuit 105.

In an example implementation, the indication 311 may be used by sequenceestimation circuit 306 to weight branch metrics and/or log-likelihoodratios generated in the sequence estimation circuit 306. Samples havingvery high signal strength may suffer from high nonlinear distortionwhich may not be accurately estimated/reproduced by circuit 105.Accordingly, branch metrics and/or log-likelihood ratios for suchsamples may be given less weight than other samples having moderatesignal strength. Similarly, samples having very low signal strength maybe very noisy. Accordingly, branch metrics and/or log-likelihood ratiosfor such samples may be given less weight than other samples havingmoderate signal strength.

The SSI 310 may be operable to measure signal strength over a band offrequencies that is wider than the desired channel. Information aboutsignal strength on adjacent channels may be used to determine likelynonlinear distortion (e.g., nonlinear distortion may cause signals onthe desired channel to spill over into adjacent channels) and/orinterference on the desired channel and, accordingly, used for weightingbranch metrics and/or log-likelihood ratios.

A source identification circuit 320 may be implemented as dedicatedcircuitry near the front-end of the receiver and/or in the digitalbaseband processing circuit 322. The source identification circuit 320is operable to determine the source of a received signal and output anindication 321 of the identity of the determined source (e.g.,indication 321 may be an IP address, MAC address, make and model number,and/or the like). The indication 321 may be used by the nonlineardistortion modeling circuit 105 to select which nonlinear distortionmodel parameter values to use for demodulating and decoding the signalfrom the determined source.

FIG. 3B depicts components of an example receiver for orthogonalfrequency division multiplexed (OFDM) communications in which adaptivenonlinear distortion models are used for improving communicationperformance.

In the OFDM receiver of FIG. 3B, there is an SSI 310 as in FIG. 3A.Additionally, or alternatively, there may be an SSI 366 which may beoperable to generate a per-OFDM subcarrier (or per-group-of-OFDMsubcarriers) indication of transmitted signal strength. The signalstrength indication(s) 311 from the SSI 310 and/or SSI 366 may be usedby the sequence estimation circuit 360 to weight branch metrics and/orlog-likelihood ratios similar to as described above with reference toFIG. 3A. In an example implementation, the signal strengthindications(s) 311 from the SSI 310 and/or RSSI 366 may be used by thenonlinear distortion modeling circuit 105 to select which nonlineardistortion model parameter values to use for demodulating and decodingthe subcarrier(s) corresponding to the signal strength indication.

In the OFDM receiver of FIG. 3B, there is a source identificationcircuit 320 as in FIG. 3A. The source identifiers 321 from the sourceidentification circuit 320 may be used by the nonlinear distortionmodeling circuit 105 to select which nonlinear distortion modelparameter values to use for demodulating and decoding the subcarrier(s)from the identified source(s).

FIG. 4 depicts components of an example receiver operable to performmutual sequence estimation of multiple concurrent streams using anadaptive nonlinear distortion model. Shown in FIG. 4 are a sequenceestimation circuit 402 which is operable to jointly estimate N symbolstreams. Each of the symbol streams 401 ₁-401 _(N) (N is an integer) mayexperience the same nonlinear distortion en route to the sequenceestimation circuit. Since each of the N streams experience the samenonlinear distortion, more streams may provide more information foradapting the nonlinear distortion model. As a result, the nonlineardistortion model may more accurately estimate/reproduce the actualnonlinear distortion experienced by the received streams, as compared toa single stream. Estimated symbols of each of M streams (M an integerless than or equal to N) output by sequence estimation circuit may beconveyed to a corresponding one of decoders 404 ₁-404 _(M).

FIG. 5 is a flowchart illustrating an example process for determiningnonlinear distortion model parameter values for a plurality of signalsources. In block 502, a receiver (e.g., 103) receives a signal from asignal source (e.g., transmitter 116 a). In block 504, the receiverdetermines (e.g., using an adaptation/training algorithm) a set ofnonlinear distortion model parameters using the received signal. Inblock 506, the receiver determines an identifier (e.g. MAC address) ofthe source of the received signal. In block 508, the receiver stores thedetermined set of nonlinear distortion model parameters to memory, andassociates them in memory with the determined identifier.

FIG. 6 is a flowchart illustrating an example process for handlingnonlinear distortion in a multiuser environment. In block 602, areceiver (e.g., 103) receives a signal from a signal source (e.g.,transmitter 116 a). In block 604, the receiver determines an identifier(e.g., MAC address or unique physical layer signaling signature) for thesource of the signal. In block 606, the receiver generates an indicationof transmitted signal strength for a sample of the received signal. Inblock 608, the receiver selects nonlinear distortion model parametervalues based on the determined identifier and based on the strengthindication for the sample. In block 610, the receiver processes thesample using the selected nonlinear distortion model parameter values.

In accordance with an example implementation of this disclosure, anelectronic receiver (e.g., 103) comprises a nonlinear distortionmodeling circuit (e.g., 105) and a nonlinear distortion compensationcircuit (e.g., 104). The nonlinear distortion modeling circuit isoperable to determine a plurality of sets of nonlinear distortion modelparameter values, where each of the sets of nonlinear distortion modelparameter values representing nonlinear distortion experienced bysignals received by the electronic receiver from a respective one aplurality of communication partners. The nonlinear distortioncompensation circuit is operable to use the sets of nonlinear distortionmodel parameter values for processing of signals from the plurality ofcommunication partners. Each of the sets of nonlinear distortion modelparameter values may comprise a plurality of values (e.g., 706)corresponding to a plurality of signal powers. The sets of nonlineardistortion model parameters may be stored in a lookup table (e.g., 702)indexed by a signal strength parameter (e.g., 704). The electronicreceiver may comprise a received signal strength indicator circuit(e.g., 310) operable to generate an indication of transmitted signalstrength for the received signal. The nonlinear distortion modelingcircuit may be operable to select an entry of the lookup table based onthe indication of transmitted signal strength. The sets of nonlineardistortion model parameters may be stored in a lookup table indexed byan identifier of signal source (e.g., by MAC address). The electronicreceiver may comprise a source identification circuit (e.g., 320)operable to identify which one of the communication partners transmittedthe signal. The nonlinear distortion modeling circuit may be operable toselect which of the sets of nonlinear distortion model parameters to usefor processing of the received signal based on the identification by thesource identification circuit.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the processes as described herein.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computing system with a program orother code that, when being loaded and executed, controls the computingsystem such that it carries out the methods described herein. Anothertypical implementation may comprise an application specific integratedcircuit or chip.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A system comprising: an electronic receivercomprising: a nonlinear distortion modeling circuit operable todetermine a plurality of sets of nonlinear distortion model parametervalues, each of said sets of nonlinear distortion model parameter valuesrepresenting nonlinear distortion experienced by signals received bysaid electronic receiver from a respective one a plurality ofcommunication partners; and a nonlinear distortion compensation circuitoperable to use said sets of nonlinear distortion model parameter valuesfor processing of signals from said plurality of communication partners.2. The system of claim 1, wherein each of said sets of nonlineardistortion model parameter values comprises a plurality of valuescorresponding to a plurality of signal powers.
 3. The system of claim 2,wherein said sets of nonlinear distortion model parameters are stored ina lookup table indexed by a signal strength parameter.
 4. The system ofclaim 3, wherein: said electronic receiver comprises a signal strengthindicator circuit operable to generate an indication of transmittedsignal strength of a received signal; and said nonlinear distortionmodeling circuit is operable to select an entry of said lookup table forprocessing of said received signal based on said indication oftransmitted signal strength of said received signal.
 5. The system ofclaim 1, wherein said sets of nonlinear distortion model parameters arestored in a lookup table indexed by an identifier of signal source. 6.The system of claim 1, said electronic receiver comprises a sourceidentification circuit operable to identify which one of saidcommunication partners transmitted said signal.
 7. The system of claim6, wherein said nonlinear distortion modeling circuit is operable toselect which of said sets of nonlinear distortion model parameters touse for processing of said received signal based on said identificationby said source identification circuit.
 8. The system of claim 1, whereinsaid nonlinear distortion modeling circuit is operable to: for eachburst transmission received, determine which one of said sets ofnonlinear distortion model parameter values to use for processing ofsaid burst based on a preamble of said burst.
 9. The system of claim 1,wherein: each set of said plurality of sets of nonlinear distortionmodel parameter values corresponds to a respective one of a plurality oftransmitters with which said electronic receiver communicates.
 10. Thesystem of claim 9, wherein said nonlinear distortion modeling circuit isoperable to determine one of said sets of nonlinear distortion modelparameter values for a particular one of said transmitters based ontraining signals sent during admission of said particular one of saidtransmitters to a network.
 11. A system comprising: an electronicreceiver configured to communicate with a first communication partnerand a second communication partner, wherein said receiver comprises:nonlinear distortion modeling circuitry operable to: determine a firstset of nonlinear distortion model parameter values that model nonlineardistortion present in signals from said first communication partner; anddetermine a second set of nonlinear distortion model parameter valuesthat model nonlinear distortion present in signals from said secondcommunication partner; and nonlinear distortion compensation circuitryoperable to: use said first set of nonlinear distortion model parametervalues for processing of signals received from said first communicationpartner; and use said second set of nonlinear distortion model parametervalues for processing of signals received from said second communicationpartner.
 12. The system of claim 11, wherein said electronic receivercomprises source identification circuitry operable to generate anindication of whether a received signal originated from said firstcommunication partner or said second partner.
 13. The system of claim 12wherein: said nonlinear distortion modeling circuitry is operable toselect between use of said first set of nonlinear distortion modelparameter values and said second set of nonlinear distortion modelparameter values for processing of said received signal; and saidselection is based on said indication.
 14. The system of claim 11,wherein said electronic receiver comprises signal strength indicatorcircuitry operable to generate an indication of transmitted signalstrength of a signal received from said first communication partner. 15.The system of claim 14, wherein said nonlinear distortion modelingcircuitry is operable to select between use of said first set ofnonlinear distortion model parameter values and said second set ofnonlinear distortion model parameter values for processing of saidreceived signal; and said selection is based on said indication oftransmitted signal strength.
 16. The system of claim 11, wherein saidfirst set of nonlinear distortion model parameters values and saidsecond set of nonlinear distortion model parameters are stored in one ormore lookup tables in said electronic receiver.
 17. A method comprising:in an electronic receiver: determining, by a nonlinear distortionmodeling circuit of said electronic receiver, a plurality of sets ofnonlinear distortion model parameter values, each of said sets ofnonlinear distortion model parameter values representing nonlineardistortion experienced by signals received by said electronic receiverfrom a respective one a plurality of communication partners; andprocessing, by a nonlinear distortion compensation circuit of saidelectronic receiver, signals from said plurality of communicationpartners using said sets of nonlinear distortion model parameter values.19. The method of claim 18, comprising storing said sets of nonlineardistortion model parameters in a lookup table of said electronicreceiver, wherein said lookup table is indexed by a signal strengthparameter.
 20. The method of claim 18, comprising storing said sets ofnonlinear distortion model parameters in a lookup table of saidelectronic receiver, wherein said lookup table is indexed by anidentifier of signal source.